1. Field of the Invention
The present invention relates to a control apparatus; specifically, it relates to a control apparatus for regulating the brightness of a panel device of an organic light emitting diode display according to the panel characteristics.
2. Descriptions of the Related Art
Since an organic light emitting displays (OLED) has advantages of self-lighting, high luminance, high contrast, and wide viewing angles, more and more studies have focused on this field. There are two types of OLEDs: active matrix organic light emitting diode (AMOLED) displays and passive matrix organic light emitting diode (PMOLED) displays. Using a storage capacitor storing written pixel data, a pixel of an AMOLED display can maintain its original brightness after the pixel has been scanned by a scan line. The pixel of a PMOLED display requires the cooperation of both a scan line and a data line to conduct the pixel for maintaining the original brightness. Since the AMOLED display has the advantage of maintaining the brightness after the pixel has been scanned, current studies mainly focus in this domain.
An AMOLED display determines its brightness according to the current that passes through its OLEDs. By controlling the gate electrode voltage of a coupled thin film transistor (TFT), various grayscale levels can be defined. Since the manufacturing process of the TFT is not stable, some drifting may occur. This means that each of the AMOLED displays may have different brightness levels, even if they are provided with the same driving current. According to experimental measurements, the difference between the brightness levels can be as high as ±25%.
The aforementioned drifting problem can be improved using a stricter processing control to reduce the characteristic drifting of the TFTs. However, this kind of approach degrades the yield rate and increases the cost of the manufacturing process. Another approach is to provide an external power supply with various voltage levels for various panels to achieve the same brightness level. However, external power supplies are designed on printed circuit boards by other suppliers, which can not be adjusted correspondingly when panels are assembled for shipping. As a result, this approach is not an effective way to solve this problem. Consequently, it is important to find a way to prevent non-uniform brightness of the panels that result from the drifting of the TFTs.